What? Are you saying Gendry run all the way from Bridge of Skulls in the west, pass by Castle Black and other castles, to collapse before Eastwatch? No, they were on the east coast, somewhere between Hardhome and Eastwatch. We know there are mountains at Hardhome. And if you watch Bran's ravens' vision from the last episode, they flew over Eastwatch and then over some mountains - why would the ravens fly over Eastwatch if they were going west from Winterfell? Btw in that vision Night King was standing on the "last stand rock".